Improved numerical simulation of non-thermal enhanced heavy oil recovery

The dependence on unconventional resources such as heavy oil is on the rise due to geometric increase in demand for energy and the decline of production from mature conventional oil reservoirs. Heavy oil reservoirs contain oil that has some limited mobility under reservoir conditions and only a small fraction of the oil-in-place can be recovered by primary technique which involve harnessing the internal reservoir energy. The remaining oil after the primary depletion is still mostly continuous and present a valuable target for enhanced recovery. However, most of these reservoirs are relatively thin, making them poor candidates for thermal methods, in addition to associated high energy requirement and adverse environmental effects of the heating process. Therefore, any incremental oil recovery must be through non-thermal methods, such as waterflooding, chemical and gas injection. These methods however suffer from adverse mobility ratio which significantly affect the efficiency of the displacement process. The simulation of these processes for the purpose of reservoir prediction and performance is a herculean task due to the complex physics of instability and compositional effect taking place that is not fully understood. In this thesis, the results of improved numerical simulation techniques of non-thermal heavy oil recovery were presented, demonstrating the viability of the techniques as simulation methods heavy oil non-thermal enhanced heavy oil recovery (EHOR). Several displacement mechanisms were identified through the simulation of the secondary and tertiary processes that contributed to significant incremental heavy oil recovery. A systematic lumping scheme of the heavy oil components into pseudo-components based on the behaviour of the produced oil was proposed. A new methodology for the estimation of relative permeability from displacement with instability and compositional effect using a two-dimensional (2D), high-resolution model to effectively capture the finger, and a versatile, three-parameter function (L.E.T correlation) was demonstrated. A semianalytical approach through a combination of theoretical and an empirical prediction method based on the famous works of Koval, and Todd and Longstaff on viscous fingering was employed for the verification of the estimated relative permeability. Lastly, a multiscale approach to history matching, for the estimation of unstable relative permeability that is computationally more efficient, was proposed. It involves the history matching of a set of coarse grid models to predict the fine-scale relative permeability. In this approach, fine-scale information was resolved without direct solution of the global fine-scale problem. The results showed that the time required to estimate relative permeability using the multiscale approach was only about 35% required to estimate the same relative permeability using a single high-resolution model. The memory requirement for the approach was also about 50% required for simulation of the single high-resolution model. Therefore, the lower memory size and computations required in the multiscale approach mean that a less powerful computer can be used to estimate the relative permeability curves for unstable displacements with accuracy similar to that obtained using a high-resolution model approach

Evaluation of Intelligent Wells Performance in a Five-Spot Arrangement

The efficiency of water flooding processes can be improved by installing intelligent wells which are good candidates for control and optimization. Optimal control theory based on adjoint formulations was found to be efficient for reservoir optimization. However, this solution approach is local and may not be suitable for comparing design alternatives. In this work, an approach for determining an optimal starting point for optimal control theory procedure was developed to give near global optima. The performance in terms of net present value (NPV) of two forms of five-spot pattern was compared. The method results to similar performances of the two alternatives because it was formulated to give true optimal solution trajectories. It was found that regular five-spot pattern results to a NPV in excess of $4,900 over inverted design. Respective increase in oil and water productions of 0.23% and 0.22% were recorded for former design against the later.Keywords: intelligent wells; adjoint; optimal control theory; global optimum; water flooding

Molecular diagnosis of urinary Mycobacterium tuberculosis among patients attending urology clinic in Aminu Kano Teaching Hospital, Kano, Nigeria

Background: Tuberculosis, a communicable disease with significant morbidity and mortality. It is still among the top killers of infectious diseases; Mycobacterium tuberculosis is a successful pathogen that has evolved several mechanisms to manipulate the host immune response. Objective of the study: The objective of this study was to determine the prevalence of urinary tuberculosis among patients attending urology clinic in Aminu Kano Teaching Hospital, Kano, Nigeria. Materials and Methods: A prospective cross-sectional laboratory based study that involved the use of questionnaire and consent/assent form prior to sample collection. Xpert MTB/Rif assay was used to analyze the urine samples. Results: The results of this study shows that, out of 71 samples analyzed along with positive control (H37RV) and molecular grade water was used as negative control. The results showed that, 2 (2.8 %) were from urine samples. Data generated were analyzed using descriptive statistics and results were presented in tables and charts. Conclusion: The study confirmed the presence of urinary tuberculosis in the study area, with prevalence of 2.8%. The pattern of tuberculosis was susceptible Mycobacterium tuberculosis. Therefore, there is need to introduce a routine screening of urinary tuberculosis among patients presenting sign and symptoms of urinary tract infection using Gene Xpert. This will be achieved through the engagement and enlightenment of the clinicians, strengthening the laboratory capacity for diagnosis and make the services available and accessible to the patients who need them. Keywords: Mycobacterium tuberculosis; Extra-Pulmonary Tuberculosis; Prevalence and Gene Xpert

Fingerprint White Line Counts: An Upcoming Forensic Tool for Sex Determination

Abstract Fingerprints are one of the common forensic tools used in personal identification. However, the associated secondary epidermal creases of fingerprints, fingerprint white line count (FWLC), has received less attention within the forensic community. This study was conducted with an aim to determine the potential of FWLC in sex inference among adult Nigerians. A cross sectional study was carried out with 150 males and 150 females with age range of 18-30 and 18-33 years, respectively. Live scanner (Digita persona, China) was used to capture the plain fingerprint for FWLC. Mann Whitney, Kruskal Wallis and logistic regression analyses were employed for determination of digit variation (based on side and type), sexual dimorphism and prediction models, respectively. Likelihood ratio and posterior probability were used to determine the favour odd for sex inference from FWLC. A significant higher mean value of FWLC was observed in females (2.24 ± 2.03) compared to males (0.85 ± 1.29). Absence of white line was indicative of male origin in all the digits except for left index digit (favor odd of 0.72 for females and 0.29 for males). However, FWLC from 5 to 11 were more likely to be of female origin. The best discriminator of sex was the left FWLC with a percentage accuracy of discrimination of 72%. The percentage contribution of the left FWLC in the discrimination of the sexes was observed to range from 23.0 to 30.20%. The FWLC was found to be a potential predictor of sex among adult Nigerians of Hausa ethnic origin

Matching of Water Breakthroughs in a Low-Resistivity Oil Reservoir Using Permeability Anisotropy

In a mature middle and lower Gharif field in Oman, uncertainties surrounding initial water saturation and early water breakthroughs of unknown sources and paths suggest the presence of significant bypassed oil. In order to determine the areas with remaining oil, petrophysical and logging data of seven wells were processed using Techlog software and imported into Petrel software for modelling and simulation. Porosity was calculated using the Electric Propagation Time log and was utilized to evaluate the presence of oil, particularly in the upper tight zone of the formation. Despite the low resistivity readings in the highly porous layers, caused by good network connectivity and high formation water salinity, the resistivity contrast was sufficient to differentiate them from the oil zone. However, the calculated water saturation (Sw) in the tight top oil zone was high, consistent with the observed water production in the field. To improve the match between production data and simulation results, sensitivity analyses were conducted on various permeability anisotropy and relative permeability values within the model. The analyses showed that core-derived permeability anisotropy (vertical to horizontal ratio of 1:1) yielded a better history match for water production compared to the conventionally used value of 1:10. Water saturation maps were generated at the start and the end of production to highlight saturation distribution within the reservoirs. The maps revealed that in the lower porous part, the oil was fully depleted around the wells but remained trapped in the undrilled areas

An improved approach to estimate three-phase relative permeability functions for heavy-oil displacement involving instability and compositional effects

Simultaneous three-phase flow of gas, oil and water is a common phenomenon in enhanced oil recovery techniques such as water-alternating-gas (WAG) injection. Reliable reservoir simulations are required to predict the performance of these injections before field application. However, heavy oil displacement by gas or water can lead to viscous fingering due to the unfavorable mobility ratio between heavy oil and the displacing fluid. In addition, the injection of partially dissolvable gases such as CO2 can result in compositional effects, which can bring about a significant reduction of oil viscosity and hence can cause variations of the mobility ratio. Estimations of three-phase relative permeability under such conditions are extremely complex, and using conventional techniques for the estimation can lead to erroneous results. We used the results of four coreflood experiments, carried out on a core, to estimate two-phase and three-phase relative permeability. A new history matching methodology for laboratory experiments was used that takes into account the instability and the compositional effects in the estimation processes. The results demonstrate that a simultaneous CO2 and water injection (CO2-simultaneous water and gas (SWAG)) can be adequately matched using the relative permeabilities of a secondary gas/liquid and a tertiary oil/water. In heavy oil WAG injection, the injected water follows the CO2 path due its lower resistance as a result of the CO2 dissolution in the oil and the resultant reduction of the oil viscosity. This is contrary to WAG injection in conventional oils, where gas and water open up separate saturations paths. It is also important to include capillary pressure (Pc), even in high permeable porous media, as we observed that the inclusion of capillary pressure dampened the propagation of the viscous fingers and hence helped the front to become stabilized, leading to a more realistic simulated sweep efficiency

An Improved Approach to Estimate Three-Phase Relative Permeability Functions for Heavy-Oil Displacement Involving Instability and Compositional Effects

Simultaneous three-phase flow of gas, oil and water is a common phenomenon in enhanced oil recovery techniques such as water-alternating-gas (WAG) injection. Reliable reservoir simulations are required to predict the performance of these injections before field application. However, heavy oil displacement by gas or water can lead to viscous fingering due to the unfavorable mobility ratio between heavy oil and the displacing fluid. In addition, the injection of partially dissolvable gases such as CO2 can result in compositional effects, which can bring about a significant reduction of oil viscosity and hence can cause variations of the mobility ratio. Estimations of three-phase relative permeability under such conditions are extremely complex, and using conventional techniques for the estimation can lead to erroneous results. We used the results of four coreflood experiments, carried out on a core, to estimate two-phase and three-phase relative permeability. A new history matching methodology for laboratory experiments was used that takes into account the instability and the compositional effects in the estimation processes. The results demonstrate that a simultaneous CO2 and water injection (CO2-simultaneous water and gas (SWAG)) can be adequately matched using the relative permeabilities of a secondary gas/liquid and a tertiary oil/water. In heavy oil WAG injection, the injected water follows the CO2 path due its lower resistance as a result of the CO2 dissolution in the oil and the resultant reduction of the oil viscosity. This is contrary to WAG injection in conventional oils, where gas and water open up separate saturations paths. It is also important to include capillary pressure (Pc), even in high permeable porous media, as we observed that the inclusion of capillary pressure dampened the propagation of the viscous fingers and hence helped the front to become stabilized, leading to a more realistic simulated sweep efficiency